An industrial vehicle such as a forklift is provided with a battery. In particular, an electric forklift (hereinafter, a battery forklift) travels by driving a traveling motor using the battery as a power source, and performs a cargo handling operation by operating a cargo handling device through the driving of a cargo handling motor. Here, when the battery is a lead storage battery, the amount of a battery liquid (electrolyte) of the battery is decreased due to the frequent repetition of the charge and discharge of the battery or the like. If the battery is discharged when the amount of the battery liquid is decreased, the degradation of the battery is facilitated. For this reason, there is a concern that the life of the battery is shortened.
In general, when batteries are connected to each other in series, charging is also performed in series. Here, if the capacity of any one of the batteries is insufficient, the amount of charge is increased so that the battery of which the capacity is insufficient is fully charged. For this reason, the other batteries of which the capacity is not insufficient are overcharged. Overcharge causes the life of the battery to be shortened.
In particular, there is a case in which the amount of a battery liquid present in the battery is decreased by electrolysis even though natural evaporation does not occur. When electrode plates of the battery are exposed to the outside due to the shortage of the battery liquid, the degradation of the electrode plates is facilitated by oxidation. As a result, the battery reaches damage. For this reason, when the battery liquid is insufficient, the battery is to be refilled with a battery replenisher.
Accordingly, Patent Literature 1 discloses an industrial vehicle that suppresses the degradation of a battery caused by discharge when the level of the battery liquid is lowered and makes an operator reliably recognize a low battery liquid level state. In particular, Patent Literature 1 discloses an industrial vehicle that stepwise limits the torque of a traveling motor according to an operating time in a low liquid level state.
Further, Patent Literature 2 discloses an industrial vehicle that is provided with a hydrogen gas-concentration sensor near a battery and prevents explosion in advance, which is caused by a hydrogen gas generated during the charge, on the basis of the hydrogen gas-concentration detected by the hydrogen gas-concentration sensor.
Furthermore, Patent Literature 3 discloses a vehicle that detects the shortage of a battery liquid by a liquid level sensor and stores a detection result as data After that, the data are processed by a computer for data processing.